The Yes and No campaigns have unveiled rival election broadcasts as the battle over how Britain elects its MPs steps up a gear.

The No campaign ad, which aired on Monday, features the odious - and fictional - MP Alan B'Stard, played by comedian Rik Mayall, to demonstrate what it says are the perils of switching to the alternative vote.

The Yes campaign ad, to be shown on TV on Tuesday, features a series of voters confronting their failing MPs while the politicians try to hide, run away or ignore them.

The two sides tossed a coin to decide who would get to show their broadcast first.

On 5 May, voters across the UK will be asked whether they want to retain first-past-the-post or switch to AV.

In the Yes film, the traditional role of would-be MP and voter is reversed, with the latter attempting to secure the former's vote for AV.

Shouting via loudhailers, the "voters" demand their politicians agree to a change because the current system sees too many holding onto a job for life without fulfilling any of their promises to constituents.

"Every time there's an election you guys show up on our doorsteps, pretend to listen, promise us the world, but nothing ever seems to change," one "voter" complains.

The film blames first-past-the-post for the expenses scandal, and shows one of the "MPs" enjoying lunch and a glass of red wine, while expressing distaste at the idea that he would have to work harder under AV.

Referring to the referendum itself, the voiceover adds: "This is the vote that makes all of our votes more powerful."

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Media captionReferendum Campaign Broadcast by the Yes campaign

The No campaign has adopted B'Stard - star of the 1980s and 90s sitcom The New Statesman - as its poster boy.

Aired on Monday, the film shows him making a series of populist election promises - "abandon all taxes, free houses for everyone" - before throwing his manifesto into a fire.

He adds: "With AV, even if they don't vote for me, I'll probably still get in."

The film claims AV will lead to "fudged coalitions" and could mean the third most popular candidate in a constituency ends up winning.

THE REFERENDUM CHOICE

At the moment MPs are elected by the first-past-the-post system, where the candidate getting the most votes in a constituency is elected.

On 5 May all registered UK voters will be able to vote Yes or No on whether to change the way MPs are elected to the alternative vote system.

Under the alternative vote system, voters rank candidates in their constituency in order of preference.

Anyone getting more than 50% of first-preference votes is elected.

If no-one gets 50% of votes, the candidate with the fewest votes is eliminated and their backers' second choices allocated to those remaining.

This process continues until one candidate has at least 50% of all votes in that round.

It demonstrates the alleged fault with AV by showing a horse race - featuring runners Tory Boy, Labour Lad and Lib Dem - in which the third placed horse, Lib Dem, is eventually handed the cup.

The final scenes show a lecturer trying and failing to explain AV to a class of confused students.

The Conservatives agreed to a referendum on AV as part of the coalition agreement, but Prime Minister David Cameron is opposed to any change.

His coalition partner Nick Clegg and Labour leader Ed Miliband are both supporting the Yes campaign.

Under first-past-the-post the candidate who gets the most votes in a constituency is elected.

In contrast, under AV voters rank candidates in their constituency in order of preference.

If no candidate wins more than 50% of the vote the candidate with the fewest votes is eliminated and their backers' second choices allocated to those remaining, with process continuing until one candidate has more than half the votes in that round.